Cardinality of indexed columns... how to discover? What is the ma

[Jeremy Pulcifer]

Title: Cardinality of indexed columns... how to discover? What is the magic number?

I'm constantly finding, in the database that I'm developing/supporting, b-tree indexes on columns with low-cardinality. I generally re-create said index as a bitmap; however I'd like to go through the entire db and identify these cases proactively. Is there a way to determine the cardinality of an index's columns via the dictionary? Also, what recommendations do you have for determining the cardinality percentage that indicates when a bitmap should be used? 10%? 20%?